This invention relates to an idle speed control actuator which is adapted to control the idle speed of a vehicle engine.
In order to minimize dangerous vehicle emissions and to maximize fuel economy, it is desirable to set the vehicle engine idle speed at its lowest possible level consistent with smooth engine operation. However, the engine idle speed cannot be set too low, because the load on the engine during idle conditions may vary substantially. For example, if the vehicle engine is being idled and the air conditioning system is turned on, the load on the vehicle engine is substantially increased, and can possibly cause the engine to stall if the butterfly valve opening in the vehicle carburetor is not adjusted accordingly to maintain a constant engine idle speed. Accordingly, it has been proposed to provide a control valve mechanism which cooperates with the vehicle throttle lever (which sets the butterfly valve opening) to vary the idle position of the throttle lever in accordance with the load on the engine, as measured by the vacuum level in the engine intake manifold. While it is necessary that the throttle control mechanism be able to respond almost instantaneously to an increase of engine load in order to prevent the vehicle engine from stalling, it is desirable to reduce the engine speed more slowly when the load is decreased or when the throttle lever is returned to the engine idle position to prevent the control mechanism from having to "hunt" the proper idle speed. Therefore, the present invention proposes an idle control mechanism in which a diaphragm is movably mounted in a housing to divide the latter into a pair of chambers, one chamber of which is connected to ambient atmosphere and the other chamber is connected to engine manifold vacuum. A check valve and orifice are provided in the vacuum line between the housing and the manifold, so that substantially uninhibited communication is permitted from the manifold to the valve, but communication in the other direction is restricted. Further, the valve mechanism includes a plunger, and a plunger spring which yieldably urges the plunger out of the housing towards the position representing maximum engine idle speed. The plunger cooperates with the diaphragm to control communication between the chambers through an orifice in the diaphragm so that, when the spring does urge the plunger towards its maximum extension position, the pressure differential across the diaphragm will be reduced, permitting the diaphragm to follow the plunger.